An acoustic wave filter is used for a filter and a duplexer that are provided in a high frequency circuit of a wireless device such as a mobile phone. There is a bulk acoustic wave (BAW) filter having a plurality of piezoelectric thin film resonators on a substrate in which a lower electrode and an upper electrode sandwich a piezoelectric film and face with each other, as an example of an acoustic wave filter.
There is known a piezoelectric thin film resonator in which a temperature compensation film that has an elastic constant of a temperature coefficient of which sign is opposite to a sign of a temperature coefficient of an elastic constant of a piezoelectric film and is inserted in the piezoelectric film in order to improve a temperature coefficient of frequency (TCF) (for example, with reference to Japanese Patent Application Publication No. S58-137317. However, there is a trade-off relationship between a temperature coefficient of frequency and an electromechanical coupling coefficient. Therefore, when a temperature compensation film is provided in order to improve the temperature coefficient of frequency, the electromechanical coefficient may be reduced. Therefore, in an acoustic wave filter using a piezoelectric thin film resonator having a temperature compensation film, a band width of the filter may be reduced. And so, there is proposed an acoustic wave filter in which there is a thickness difference of a temperature compensation film between a series resonator and a parallel resonator (with reference to Japanese Patent Application Publication No. 2004-193929). And, in order to adjust a frequency of the series resonator and the parallel resonator, there is proposed a structure in which a thickness of a frequency adjusting layer on an upper electrode of a series resonator is different from that of the frequency adjusting layer on an upper electrode of a parallel resonator (with reference to Japanese Patent Application Publication No. 2002-268644).